The present invention relates generally to improved time keeping for utility meters, and more particularly, to adaptively calibrating a real-time clock in a utility meter responsive to inaccuracy in the real-time clock during operation of the meter.
Utility meters are devices that, among other things, measure the consumption of a utility provided commodity, such as electric energy, gas, or water, by a residence, factory, commercial establishment or other such facility. Utility service providers employ utility meters to track individual customers"" usage of utility provided commodities. Utilities track customer usage for many purposes, including billing and tracking demand for the relevant consumed commodity.
Increasingly, utility service providers prefer utility meters that employ electronic circuitry to perform measurement and communications operations. Electronic circuitry reduces the number of moving parts required to perform measurement operations, resulting in increased accuracy as well as higher reliability. Further, a utility meter is typically installed at or near the facility or residence of each customer. As a result, service providers historically needed field technicians or xe2x80x9cmeter-readersxe2x80x9d to obtain data from the remotely located utility meters. Such manual meter reading imposes significant labor costs and is vulnerable to transportation problems and human error. Electronic circuitry also addresses this problem by allowing utility meters to communicate metering data and other information (such as, for example, various diagnostic data) to remote, central facilities, whereby large numbers of utility meters may be read remotely without human meter-readers.
Utility meters having electronic circuitry increasingly require accurate real-time clocks in order to function properly. For example, some meters store time correlated data for the purposes of charging customers different rates depending on the times of day when particular amounts of electricity are consumed. Such metering operations are typically referred to as xe2x80x9ctime of usexe2x80x9d metering. Time of use metering requires a highly accurate clock to ensure accurate billing.
Another type of metering that is sensitive to clock inaccuracy is demand metering. In demand metering, a customer may be charged based on the customer""s highest usage rate over any demand period within a billing cycle. A demand period is a finite time period, such as 15 minutes or an hour. An inaccurate clock can substantially degrade demand meter data, thereby resulting in significant overcharging or undercharging.
Generally, utilities have relied on two techniques to maintain time keeping accuracy in their meters: factory calibration and field synchronization. Essentially, factory calibration adjusts the rate at which time keeping devices accrue time. Traditional calibration techniques require special factory test equipment and access to components of the time keeping devices. While factory calibration settings can compensate for initial inaccuracies of the time keeping devices, factory calibration cannot accurately take into account factors that affect the accuracy of the time keeping devices over time.
By contrast, field synchronization involves periodically resetting the meter""s accrued real-time value to match a standard real-time value. In some utility meters, field synchronization involves communication circuitry that communicates with remote facilities to automatically obtain the synchronization data from remote standard clocks. Nevertheless, the effectiveness of synchronization is limited because a poorly calibrated time keeping devices will still gain or lose significant amounts of time between synchronizations.
As a result, conventional methods of factory calibration and field synchronization of time keeping devices in utility meters still require undesirably frequent removal of the utility meters from the field for recalibrations and/or undesirably frequent field synchronization communications.
Accordingly, there is a need for an improved technique for maintaining time keeping accuracy in utility meters which reduces requirements to remove the utility meters from the field for recalibrations and reduces the required frequency of field synchronization communications. There is a further need for a utility meter which employs such a technique.
The present invention fulfills the above need, as well as others, by utilizing an adaptive calibration that automatically adjusts the calibration of the real-time clock of a utility meter. In other words, the adaptive calibration of the present invention automatically adjusts the rate at which the real-time clock operates. To this end, accrued clock error is measured with reference to a time standard. The meter automatically adjusts its time keeping calibration based on the measured clock error. As a result, long term error inducing effects, such as those due to variable environmental conditions and component aging, may be compensated to reduce the clock error.
In accordance with one embodiment of the present invention, a utility meter includes a source of commodity consumption information, a timing circuit, a communication circuit, and a controller. The timing circuit is operable to generate timing signals, and the communication circuit is operable to receive externally generated reference time values. The controller is operably coupled to: the source of commodity consumption information to receive commodity consumption information therefrom; the timing circuit to receive timing signals therefrom; and the communication circuit to obtain the externally generated reference time values therefrom. Further, the controller is operable to: generate metering information based at least in part on the commodity consumption information; generate a first real-time value based at least in part on an externally generated first reference time value; derive a subsequent second real-time value, based at least in part on the first real-time value, the timing signals, and a timing circuit calibration value; obtain an externally generated second reference time value; determine a rate adjustment based at least in part on a difference between the second real-time value and the second reference time value; and generate a subsequent real-time value based at least in part on the timing signals, the timing circuit calibration value, and the rate adjustment.
In accordance with another embodiment of the present invention, an arrangement for adaptive time keeping in a utility meter is provided. The arrangement comprises a timing circuit and a controller. The timing circuit is operable to generate timing signals. The controller is operably coupled to the timing circuit to receive timing signals therefrom. Further, the controller is operable to: generate a first real-time value based at least in part on an externally generated first reference time value; derive a subsequent second real-time value, based at least in part on the first real-time value, the timing signals, and a timing circuit calibration value; obtain an externally generated second reference time value; determine a rate adjustment based at least in part on a difference between the second real-time value and the second reference time value; and generate a subsequent real-time value based at least in part on the timing signals, the timing circuit calibration value, and the rate adjustment.
In accordance with another embodiment of the present invention, a method of adaptively calibrating a real-time clock within a utility meter is provided. The method comprises: generating a first real-time value based at least in part on an externally generated first reference time value; deriving a subsequent second real-time value based at least in part on the first real-time value, the timing signals, and a timing circuit calibration value; obtaining an externally generated second reference time value; determining a rate adjustment based at least in part on a difference between the second real-time value and the second reference time value; and generating a subsequent real-time value based at least in part on the timing signals, the timing circuit calibration value, and the rate adjustment.
Thus, by generating timing circuit rate adjustments base on differences between externally generated elapsed time values and elapsed time values calculated within the meter, the utility meter according to the present invention automatically and adaptively calibrates its real-time time keeping circuitry responsive to observed errors in the real-time kept in the meter during operation. This reduces requirements to remove the meter from the field for recalibrations and can reduce the required frequency of field synchronization communications.
The above discussed features and advantages, as well as others, may be readily ascertained by those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.